Liquid ejection apparatus

CROSS REFERENCE TO RELATED APPLICATION

0001The present application claims priority from Japanese Patent Application No. 2012-047727, which was filed on Mar. 5, 2012, the disclosure of which is herein incorporated by reference to its entirety.

BACKGROUND OF THE INVENTION

00021. Field of the Invention

0003The present invention relates to a liquid ejection apparatus which has a first head to eject a first liquid including pigments and a second head to eject a second liquid including no pigments.

00042. Description of Related Art

0005There is known an inkjet printer having a head (a first head) which ejects ink (a first liquid including pigments) and another head (a second head) which ejects a print-performance enhancing liquid (a second liquid including no pigments).

0006There is also known such a technique that a purging is performed in order for a plurality of heads which eject liquids different from each other. The purging is an operation to discharge a liquid from nozzles or ejection openings of a head and leads to recovering of the ejection performance of the head. While the purging is not performed, the nozzles are covered by a preservation cap in order to prevent drying.

SUMMARY OF THE INVENTION

0007In a case where the purging is performed for the first head and the second head, it can be considered that, in a certain purging period which consists of a combination of at least one first purging that is a purging for the first head and at least one second purging that is a purging for the second head, a sequence (in which the first purging and the second purging are alternately performed and the second purging is performed after the first purging) is performed m number of times (m: natural number). The present inventor noticed that the following problems occur in this case.

0008A first problem is due to a discharge amount of the second liquid. Since the second liquid does not include pigments, the recovery degree by one purging is high. Therefore, a purging for the second head may be performed a smaller number of times than a purging for the first head, but in the above-mentioned case, the first purging and the second purging are performed the same number of times. In other words, the second liquid is uselessly discharged.

0009A second problem is due to drying of the nozzles of the first head. From the nozzles of the first head, the first liquid including pigments is ejected. Since the first liquid is directly related to a print quality, it is especially necessary that the nozzles of the first head be prevented from drying. In the above-mentioned case, at the end of the certain purging period, the second purging is performed. Since the first head is not covered by a cap in the last second purging, drying of the nozzles of the first head increases.

0010It is therefore an object of the present invention to provide a liquid ejection apparatus to reduce the discharge amount of the second liquid and to restrain drying of the nozzles of the first head.

0011In order to achieve the above-mentioned object, according to the present invention, there is provided a liquid ejection apparatus comprising: a first head having a plurality of nozzles from which a first liquid including pigments is ejected; a second head having a plurality of nozzles from which a second liquid including no pigments is ejected; a cap device configured to be selectively positioned at a capping position where the cap device covers the plurality of nozzles of the first head and the plurality of nozzles of the second head, and at an uncapping position where the cap device does not cover the plurality of nozzles of the first head and the plurality of nozzles of the second head; a purging executing portion configured to perform a first purging in which the first liquid is discharged from the plurality of nozzles of the first head and a second purging in which the second liquid is discharged from the plurality of nozzles of the second head, and to perform the first purging greater in number of times than the second purging in a certain purging period constituted by a combination of at least one first purging and at least one second purging and to perform the first purging as the last purging operation in the certain purging period; and a cap controller configured to control a position of the cap device so as to be positioned at the uncapping position in the certain purging period and at the capping position at least in periods before and after the certain purging period.

BRIEF DESCRIPTION OF THE DRAWINGS

0012The above and other objects, features, advantages and technical and industrial significance of the present invention will be better understood by reading the following detailed description of a preferred embodiment of the invention, when considered in connection with the accompanying drawings, in which:

0013<figref idref="DRAWINGS">FIG. 1</figref> is a cross-sectional view schematically showing an internal structure of an inkjet printer as a first embodiment to which the present invention is applied;

0014<figref idref="DRAWINGS">FIG. 2</figref> is a plan view showing a channel unit included in respective heads of the printer shown in <figref idref="DRAWINGS">FIG. 1</figref>;

0015<figref idref="DRAWINGS">FIG. 3</figref> is an enlarged view showing an area III enclosed by a one-dot chain line in <figref idref="DRAWINGS">FIG. 2</figref>;

0016<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view taken along a line IV-IV in <figref idref="DRAWINGS">FIG. 3</figref>;

0017<figref idref="DRAWINGS">FIG. 5A</figref> and <figref idref="DRAWINGS">FIG. 5B</figref> are illustrative views for explaining operations of a cap and a support mechanism;

0018<figref idref="DRAWINGS">FIG. 6</figref> is a block diagram showing an electrical structure of the printer;

0019<figref idref="DRAWINGS">FIG. 7</figref> is a flow chart showing a purging control implemented by the controller; and

0020<figref idref="DRAWINGS">FIGS. 8A through 8C</figref> are explanatory views showing respective purging patterns in a certain purging period and correspond to the first, a second and a third embodiments, respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

0021There will be described preferred embodiments of the invention with reference to the drawings.

0022There will be described an overall structure of an inkjet printer <b>1</b> as a first embodiment to which the present invention is applied with reference to <figref idref="DRAWINGS">FIG. 1</figref>.

0023The inkjet printer <b>1</b> includes a casing <b>1</b><i>a </i>having a rectangular parallelepiped shape. In an upper portion of a top panel of the casing <b>1</b><i>a</i>, there is disposed a sheet-discharge portion <b>31</b>. In an inner space of the casing <b>1</b><i>a</i>, there is formed a conveying path through which a recording sheet P is conveyed from a sheet-supply unit <b>1</b><i>c </i>to the sheet-discharge portion <b>31</b> along a thick arrow A in <figref idref="DRAWINGS">FIG. 1</figref>.

0024In a lower space of the casing la and below the sheet-supply unit <b>1</b><i>c</i>, there are disposed cartridges <b>2</b><i>a</i>, <b>2</b><i>b</i>. The cartridge <b>2</b><i>a </i>stores a pretreatment liquid as an example of a second liquid and the cartridge <b>2</b><i>b </i>stores a black ink as an example of a first liquid. While the pretreatment liquid does not contain pigments, the black ink contains pigments. The pretreatment liquid is a liquid having functions to prevent ink being blurred and bled and to enhance a chromogenic effect and a fast-drying effect by coagulating pigment particles in ink, and so forth. The pretreatment liquid may contain multivalent metal salt such as cationic polymer, magnesium salt and so on. The cartridges <b>2</b><i>a</i>, <b>2</b><i>b </i>are respectively communicated to a pretreatment-liquid ejection head <b>10</b><i>a </i>as an example of a second head and an inkjet head <b>10</b><i>b </i>as an example of a first head via tubes or the like. A controller <b>1</b><i>p </i>controls pumps <b>10</b>Pa, <b>10</b>Pb (shown in <figref idref="DRAWINGS">FIG. 6</figref>) such that liquids in the cartridges <b>2</b><i>a</i>, <b>2</b><i>b </i>are timely supplied to corresponding heads <b>10</b><i>a</i>, <b>10</b><i>b. </i>

0025In the inner space of the casing la, there are accommodated the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>, the controller <b>1</b><i>p</i>, a conveyor unit <b>20</b>, a support mechanism <b>5</b> and opposing members <b>42</b> that are disposed below the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>, the sheet-supply unit <b>1</b><i>c</i>, and so forth.

0026The heads <b>10</b><i>a</i>, <b>11</b><i>a</i>, having the same structure, are line-type heads having a generally rectangular parallelepiped shape extending in a main scanning direction (a direction perpendicular to a sheet plane of <figref idref="DRAWINGS">FIG. 1</figref>). When recording (image forming), the pretreatment liquid and the black ink (hereinafter these may be generally referred to as liquid) are respectively ejected from lower surfaces (ejection surfaces <b>10</b><i>x</i>) of the corresponding heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. The heads <b>10</b><i>a</i>, <b>10</b><i>b </i>are arranged side by side in a sub-scanning direction (a direction perpendicular to the main scanning direction and a vertical direction) at a predetermined pitch and supported by the casing <b>1</b><i>a </i>via a holder <b>3</b>. The holder <b>3</b> also supports annular members <b>41</b> that are disposed corresponding to the respective heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. The annular member <b>41</b> is a member formed annularly so as to enclose an outer circumference of the ejection surface <b>10</b><i>x </i>in its plan view.

0027The opposing member <b>42</b> is a rectangular plate that is slightly larger than the annular member <b>41</b> and is composed of a material which does not absorb water (moisture) or is hard to absorb water such as glass, metal (e.g., SUS) or the like. The annular member <b>41</b> and the opposing member <b>42</b> form a cap <b>40</b> as an example of a cap device. The cap <b>40</b> will be described in detail later.

0028The support mechanism <b>5</b> consists of two platens <b>6</b><i>a</i>, <b>6</b><i>b</i>. The platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are pivotable (rotatable) about respective shafts <b>7</b><i>a</i>, <b>7</b><i>b</i>. Under control of the controller <b>1</b><i>p</i>, the platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are pivotable between a support-surface-forming position (shown in <figref idref="DRAWINGS">FIG. 1</figref>) and an open position (shown in <figref idref="DRAWINGS">FIG. 5B</figref>) by driving of a platen rotation motor <b>5</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>). At the support-surface-forming position, respective ends of the platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are opposed to each other such that the platens <b>6</b><i>a</i>, <b>6</b><i>b </i>form a support surface <b>5</b><i>a </i>which supports the recording sheet P at a position opposed to the ejection surface <b>10</b><i>x</i>. The support surface <b>5</b><i>a </i>is a flat surface as a whole. The platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are positioned at the support-surface-forming position when recording and the platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are positioned at the open position when maintenance is performed.

0029In the present embodiment, the maintenance includes a capping, a purging, a wiping, and so on. The maintenance will be described in detail later.

0030The conveyor unit <b>20</b> includes pairs of rollers <b>22</b>, <b>23</b>, <b>24</b>, <b>25</b>, <b>26</b>, <b>27</b>, guides <b>29</b><i>a</i>, <b>29</b><i>b</i>, <b>29</b><i>c</i>, <b>29</b><i>d</i>, <b>29</b><i>e </i>and an intermediate roller <b>21</b>.

0031The pairs of rollers <b>22</b> through <b>27</b> are arranged in this order from an upstream side in a conveying direction so as to form the conveying path from the sheet-supply unit <b>1</b><i>c </i>to the sheet-discharge portion <b>31</b>. Lower rollers <b>23</b><i>b</i>, <b>24</b><i>b</i>, and <b>25</b><i>b </i>of the pairs of rollers <b>23</b> through <b>25</b> are connected to a conveyor motor <b>20</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>). One of the pair of rollers <b>26</b> and one of the pair of rollers <b>27</b> are connected to the conveyor motor <b>20</b>M. The rollers connected to the conveyor motor <b>20</b>M are driving rollers rotated by driving of the conveyor motor <b>20</b>M under control of the controller <b>1</b><i>p</i>. Upper rollers <b>23</b><i>a</i>, <b>24</b><i>a </i>and <b>25</b><i>a </i>and the other rollers of the pairs of rollers <b>26</b>, <b>27</b> are driven rollers.

0032The guides <b>29</b><i>a </i>through <b>29</b><i>e </i>are arranged in this order from the upstream side in the conveying direction between the sheet-supply unit <b>1</b><i>c </i>and the pair of rollers <b>22</b>, the pair of rollers and so on so as to form the conveying path. Each of the guides <b>29</b><i>a </i>through <b>29</b><i>e </i>is composed of a pair of plates that are spaced from each other in a planar direction.

0033The intermediate roller <b>21</b> is located between the head <b>10</b><i>a </i>and the pair of rollers <b>24</b> and on an upper side of the conveying path.

0034The sheet-supply unit <b>1</b><i>c </i>includes a sheet-supply tray <b>1</b><i>c</i><b>1</b> and a sheet-supply roller <b>1</b><i>c</i><b>2</b>. The sheet-supply tray <b>1</b><i>c</i><b>1</b> is detachably attached to the casing <b>1</b><i>a </i>in the sub-scanning direction. The sheet-supply tray <b>1</b><i>c</i><b>1</b> is a box-like structure opening upward and can accommodate the recording sheets P with a plurality of sizes. The sheet-supply roller <b>1</b><i>c</i><b>2</b> is rotated by driving of a sheet-supply motor <b>1</b><i>c</i>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>) under the control of the controller <b>1</b><i>p </i>so as to supply an uppermost one of the recording sheets P in the sheet-supply tray <b>1</b><i>c</i><b>1</b>.

0035The controller <b>1</b><i>p </i>includes, in addition to a CPU (Central Processing Unit) as an arithmetic processing unit, a ROM (Read Only Memory), a RAM (Random Access Memory: including a non-volatile RAM), an ASIC (Application Specific Integrated Circuit), an I/F (Interface), an I/O (Input/Output Port), and so forth. The ROM stores programs that are executed by the CPU, various fixed data, and so on. The RAM temporality stores data (image data and so on) necessary when executing of the programs. In the ASIC, rewriting, sorting of the image data, and so on, e.g., signal processing and image processing, are performed. The I/F transmits and receives data to and from an external device. The I/O performs input/output of detection signals of various sensors.

0036Based on recording command supplied from the external device such as a PC connected to the printer <b>1</b>, the controller <b>1</b><i>p </i>controls preparation operations related to recording, supplying/conveying/discharging operations of the recording sheet P, liquid ejection which is synchronized with the conveying of the recording sheet P, and so forth such that an image is recorded on the recording sheet P. The recording sheet P supplied from the sheet-supply unit <b>1</b><i>c</i>, nipped by the pair of rollers <b>22</b> through <b>27</b>, passes through a space between the guides <b>29</b><i>a </i>through <b>29</b><i>e </i>and is conveyed in the conveying direction. When the recording sheet P passes right below the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>, in order, while supported on the support surfaces <b>5</b><i>a</i>, the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>are driven by the control of the controller <b>1</b><i>p </i>to eject the liquid to a surface of the recording sheet P from nozzles <b>14</b><i>a </i>(shown in <figref idref="DRAWINGS">FIG. 3</figref>) on the respective ejection surfaces <b>10</b><i>x</i>, so that an image is recorded on the recording sheet P. The liquid ejection from the nozzles <b>14</b><i>a </i>is performed based on detection signals from a sheet sensor <b>32</b> which detects a (leading) end of the recording sheet P. After image recording, the recording sheet P is conveyed upward and discharged from an opening <b>30</b> that is formed on an upper portion of the casing <b>1</b><i>a </i>to the sheet-discharge portion <b>31</b>.

0037Hereinafter, structures of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>will be described in detail with reference to <figref idref="DRAWINGS">FIGS. 2 through 4</figref>.

0038Each of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>includes a reservoir unit and a channel unit <b>12</b> which are stacked on each other in a vertical direction, eight actuator units <b>17</b> which are fixed to an upper surface <b>12</b><i>x </i>of the channel unit <b>12</b>, a FPC (Flexible Printed Circuit board) <b>19</b> which are connected (bonded) to the respective actuator units <b>17</b>, and so on. In the reservoir unit, there is formed a channel including a reservoir. The reservoir temporarily stores liquid supplied from corresponding accommodating portions of the cartridges <b>2</b><i>a</i>, <b>2</b><i>b</i>. In the channel unit <b>12</b>, there are formed channels extending from a plurality of openings <b>12</b><i>y </i>formed on the upper surface <b>12</b><i>x </i>to each of the plurality of nozzles <b>14</b><i>a </i>formed on a lower surface (the ejection surface <b>10</b><i>x</i>). The actuator unit <b>17</b> includes a piezoelectric actuator for each nozzle <b>14</b><i>a. </i>

0039A lower surface of the reservoir unit has a concave portion and a convex portion. The convex portion of the reservoir unit is adhered to an area of the upper surface <b>12</b><i>x </i>of the channel unit <b>12</b> so as to avoid the actuator units <b>17</b>. More specifically, an area including the openings <b>12</b><i>y </i>enclosed by a two-dot chain line shown in <figref idref="DRAWINGS">FIG. 2</figref> is the area to which the convex portion is adhered. On a (lower) surface of the convex portion, there are formed a plurality of openings that are connected to the reservoir and are opposed to the corresponding openings <b>12</b><i>y</i>. Accordingly, via the above-mentioned openings, liquid is supplied from the reservoir to the channel unit <b>12</b>. The concave portion of the reservoir unit is opposed to the upper surface <b>12</b><i>x </i>of the channel unit <b>12</b>, upper surfaces of the actuator units <b>17</b> and an upper surface of the FPC <b>19</b> with a slight clearance being made therebetween.

0040The channel unit <b>12</b> has a laminar structure which includes nine rectangular metallic plates <b>12</b><i>a</i>, <b>12</b><i>b</i>, <b>12</b><i>c</i>, <b>12</b><i>d</i>, <b>12</b><i>e</i>, <b>12</b><i>f</i>, <b>12</b><i>g</i>, <b>12</b><i>h</i>, <b>12</b><i>i </i>(shown in <figref idref="DRAWINGS">FIG. 4</figref>) having the generally same size that are stacked on, and adhered to, each other. A channel formed in the channel unit <b>12</b> includes a manifold channel <b>13</b> having the opening <b>12</b><i>y </i>at one of opposite ends thereof, a sub-manifold channel <b>13</b><i>a </i>that is branched from the manifold channel <b>13</b>, and an individual channel <b>14</b> extending from an outlet of the sub-manifold channel <b>13</b><i>a </i>to each nozzle <b>14</b><i>a </i>via a pressure chamber <b>16</b>. The individual channel <b>14</b> is formed for each nozzle <b>14</b><i>a </i>and includes an aperture <b>15</b> functioning as a throttle valve for adjusting a channel resistance. In adhesion areas of the upper surface <b>12</b><i>x </i>of the channel unit <b>12</b> to which the actuator units <b>17</b> are respectively adhered, generally rhombic-shaped openings through which the pressure chambers <b>16</b> are exposed are arranged like a matrix. In areas of the lower surface (the ejection surface <b>10</b><i>a</i>) corresponding to the adhesion areas, the nozzles <b>14</b><i>a </i>are arranged like a matrix in the same manner as the arrangement of the pressure chambers <b>16</b>.

0041In <figref idref="DRAWINGS">FIG. 3</figref>, the plurality of pressure chambers <b>16</b> and a plurality of apertures <b>15</b> are indicated by solid lines, though the pressure chambers <b>16</b> and the apertures <b>15</b> should be shown by broken lines because these are located below the actuator units <b>17</b>.

0042The actuator units <b>17</b>, each of which has a trapezoidal shape in its plan view, are arranged in two rows and in a zigzag or a staggered manner. Each actuator unit <b>17</b> covers corresponding ones of a multiplicity of openings of the pressure chambers <b>16</b>. The actuator unit <b>17</b> consists of a piezoelectric layer, an oscillating plate, a common electrode and individual electrodes, which are not shown. The piezoelectric layer, the oscillating plate and the common electrode have a trapezoidal shape of a size that defines an external configuration of the actuator unit <b>17</b>. The individual electrodes are disposed for each pressure chamber <b>16</b> and are opposed to the corresponding pressure chambers <b>16</b> on an upper surface of the piezoelectric layer. The oscillating plate is disposed between the common electrode and the pressure chambers <b>16</b>. A portion of the actuator unit <b>17</b> corresponding to each individual electrode functions as a certain piezoelectric actuator. Each actuator is individually deformable by applying of voltage via the FPC <b>19</b> so as to change a volume of the corresponding pressure chamber <b>16</b> and apply energy to liquid in the pressure chamber <b>16</b>. Accordingly, liquid is ejected from the nozzles <b>14</b><i>a. </i>

0043The FPC <b>19</b> has wires corresponding to the respective electrodes of the actuator units <b>17</b>, and a driver IC is mounted on a middle portion of each wire of the FPC <b>19</b>. One end portion of (each wire of) the FPC <b>19</b> is connected to the corresponding actuator units <b>17</b>, and the other is connected to circuit boards of the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. The circuit board adjusts signals inputted from the controller <b>1</b><i>p </i>and outputs the adjusted signals to the driver IC via the wires of the FPC <b>19</b>. The driver IC converts the signals inputted from the circuit board into drive signals and transmits the drive signals to each electrode of the actuator units <b>17</b> via the wires of the FPC <b>19</b>.

0044Hereinafter, a structure of the cap <b>40</b>, the capping operation, the purging operation and so on will be described with reference to <figref idref="DRAWINGS">FIGS. 5A and 5B</figref>.

0045The annular member <b>41</b> is connected to a plurality of gears <b>43</b>, and the plurality of gears <b>43</b> are rotated by driving of an annular-member lifting motor <b>41</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>) under the control of the controller <b>1</b><i>p </i>such that the annular member <b>41</b> moves up and down. One end (a lower end) of the annular member <b>41</b> is movable up and down and the other end (a base end) is fixed to a side surface of each of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>along its circumference.

0046The opposing member <b>42</b> is connected to an opposing-member lifting motor <b>42</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>) and moves up and down by driving of the opposing-member lifting motor <b>42</b>M under the control of the controller <b>1</b><i>p</i>. The opposing member <b>42</b> can be positioned at either one of a first, a second and a third positions. The first position is located at the highest (uppermost) position, the third position is at the lowest position, and the second position is located at a position lower than the first position and higher than the third position. The opposing member <b>42</b> is positioned at the first position during the capping, at the second position during the purging, at the third position during the recording or on standby. When the opposing member <b>42</b> is positioned at the first position, a distance between an opposing surface <b>42</b><i>a </i>(a surface of the opposing member <b>42</b> and a surface opposed to the ejection surface <b>10</b><i>x </i>when the platens <b>6</b><i>a</i>, <b>6</b><i>b </i>are at the open position) and the ejection surface <b>10</b><i>x </i>is equal to a distance between the support surface <b>5</b><i>a </i>and the ejection surface <b>10</b><i>x </i>when the recording.

0047The cap <b>40</b> can be positioned at a capping position (<figref idref="DRAWINGS">FIG. 5B</figref>) where an ejection space V<b>1</b> opposed to the ejection surface <b>10</b><i>x </i>of the corresponding one of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>is defined such that the cap <b>40</b> covers the nozzles <b>14</b><i>a</i>. The cap <b>40</b> can be positioned at an uncapping position (<figref idref="DRAWINGS">FIG. 1</figref> and <figref idref="DRAWINGS">FIG. 5A</figref>) where the ejection space V<b>1</b> of the corresponding one of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>is opened such that the cap <b>40</b> does not cover the nozzles <b>14</b><i>a</i>. When the cap <b>40</b> is positioned at the capping position, a clearance between the ejection surface <b>10</b><i>x </i>and the opposing surface <b>42</b><i>a </i>is defined by the annular member <b>41</b> as the ejection space V<b>1</b>.

0048The capping means that the cap <b>40</b> is kept at the capping position. In the present embodiment, in a case where the cap <b>40</b> is positioned at the capping position, as shown in <figref idref="DRAWINGS">FIG. 5B</figref>, the controller <b>1</b><i>p </i>makes the annular member <b>41</b> move down in a state in which the support mechanism <b>5</b> is positioned at the open position and the opposing member <b>42</b> is positioned at the first position. Accordingly, the lower end <b>41</b><i>a </i>of the annular member <b>41</b> is held in contact with the opposing surface <b>42</b><i>a </i>so as to define the ejection space V<b>1</b>. The capping operation is performed, for example, when the recording command has not been received for a period of time equal to or longer than a predetermined period of time, and so forth. Because the ejection space V<b>1</b> is defined by the capping operation, the ejection space V<b>1</b> is prevented from drying and viscosity (thickening) of liquid in the nozzles <b>14</b><i>a </i>is restrained.

0049On the capping operation, the two annular members <b>41</b> corresponding to the respective heads <b>10</b><i>a</i>, <b>10</b><i>b </i>are simultaneously driven, and the two opposing members <b>42</b> corresponding to the respective heads <b>10</b><i>a</i>, <b>10</b><i>b </i>are also driven simultaneously. In this case, simplified structure and control can be realized, compared to a case where composing elements of the cap <b>40</b> are driven independently for each heads <b>10</b><i>a</i>, <b>10</b><i>b. </i>

0050The purging operation is an operation in which liquid is sent to the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>by driving of pumps <b>10</b>Pa, <b>10</b>Pb (shown in <figref idref="DRAWINGS">FIG. 6</figref>) such that the liquid is forcibly discharged from the nozzles <b>14</b><i>a</i>. The liquid discharged by the purging operation is received on the opposing surfaces <b>42</b> of the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. Due to the purging operation, thicken liquid and liquid containing foreign matters (dusts, bubbles, and so on) in the nozzles <b>14</b><i>a </i>are discharged, so that the ejection performance can be recovered.

0051Though the pumps <b>10</b>Pa, <b>10</b>Pb are respectively provided for the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>, a power source for the purging operation is common to the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. Switching of a purging object (the head <b>10</b><i>a </i>or the head <b>10</b><i>b</i>) is made by a switching mechanism to which planetary gears are applied.

0052After the purging operation, the wiping operation is performed. The wiping operation is an operation in which a plate-like wiper made of an elastic material such as rubber and so forth is moved relative to an object (ejection surface <b>10</b><i>x </i>or the opposing surface <b>42</b><i>a</i>), in a state in which the wiper is in contact with the object such that foreign matters on the object are removed. The wiping operation includes a wiping on the ejection surface <b>10</b><i>x </i>and a wiping on the opposing surface <b>42</b><i>a</i>. Depending on a structure of the wiper, the wiping on the opposing surface <b>42</b><i>a </i>may be performed after the wiping on the ejection surface <b>10</b><i>x</i>, or the wiping on the ejection surface <b>10</b><i>x </i>and the wiping on the opposing surface <b>42</b><i>a </i>may be performed simultaneously. There are disposed respective wipers corresponding to the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. The respective wipers are moved in a lengthwise direction of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>(in the main scanning direction) in the wiping operation and moved back to a waiting position after the wiping operation. The waiting position of the wiper is located in the vicinity of one end of the heads <b>10</b><i>a</i>, <b>10</b><i>b </i>in the lengthwise direction.

0053Though the wipers are respectively provided for the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>, a power source for the wiping operation is common to the heads <b>10</b><i>a</i>, <b>10</b><i>b</i>. Switching of a wiping object (the ejection surface <b>10</b><i>x </i>or the opposing surface <b>42</b><i>a</i>) is made by another switching mechanism to which planetary gears are applied.

0054The purging and the wiping is performed as a set for each heads <b>10</b><i>a</i>, <b>10</b><i>b. </i>

0055Hereinafter, a purging control executed by the controller <b>1</b><i>p </i>will be described with reference to <figref idref="DRAWINGS">FIGS. 7 and 8A</figref>.

0056The controller <b>1</b><i>p </i>first determines whether a purging command is received (step <b>1</b>: hereinafter “step” is omitted and referred to as “S”, S<b>1</b>). In a case where the capping operation continues for a period equal to or longer than a predetermined period of time, the controller <b>1</b><i>p </i>receives the purging command.

0057When the controller <b>1</b><i>p </i>has received the purging command (S<b>1</b>: YES), the controller <b>1</b><i>p </i>makes the cap <b>40</b> to be positioned at the capping position (S<b>2</b>). At the time, as shown in <figref idref="DRAWINGS">FIG. 5B</figref>, the controller <b>1</b><i>p </i>keeps the support mechanism <b>5</b> at the open position and the opposing member <b>42</b> at the first position, and the controller <b>1</b><i>p </i>controls the annular-member lifting motor <b>41</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>) to drive to rotate the gears such that the annular member <b>41</b> moves up. Thus, the lower end <b>41</b><i>a </i>of the annular member <b>41</b> is distanced from the opposing surface <b>42</b><i>a </i>and the ejection space V<b>1</b> is opened. The controller <b>1</b><i>p </i>then makes the opposing member <b>42</b> move to the second position by driving of the opposing-member lifting motor <b>42</b>M.

0058The controller <b>1</b><i>p </i>performs the purging operation after execution of S<b>2</b> (S<b>3</b>). At the time, the controller <b>1</b><i>p </i>keeps the support mechanism <b>5</b> at the open position, the opposing member <b>42</b> at the second position, and the cap <b>40</b> at the uncapping position, and the controller <b>1</b><i>p </i>controls driving of the pumps <b>10</b>Pa, <b>10</b>Pb and so forth so as to realize a purging pattern shown in <figref idref="DRAWINGS">FIG. 8A</figref>. In the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, first a Bk purging (a purging for the inkjet head <b>10</b><i>b</i>; an example of a first purging) is performed n times consecutively (n: natural number equal to or greater than 2), and then, a sequence in which one Bk purging is performed following one Pr purging (a purging for the pretreatment-liquid ejection head <b>10</b><i>a</i>; an example of a second purging) is performed m times (m: natural number). After each of the purgings (each of the Bk purgings and each of the Pr purgings), the wiping is performed as described before. In the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, in a certain purging period constituted by a combination of at least one Bk purging and at least one Pr purging, the number of times of the at least one Bk purging is greater than that of the at least one Pr purging and the Bk purging is performed as the last purging. The driving number of times of the pumps <b>10</b>Pa, <b>10</b>Pb in each of the Bk purging and the Pr purging can be properly determined.

0059Further, in a case where it is defined that a first purging period is a period necessary for the first purging (the Bk purging) to be performed once and a second purging period is a period necessary for the second purging (the Pr purging) to be performed once, the certain purging period necessary for the purging operation consisting of the combination of the at least one Bk purging and the at least one Pr purging is a period substantially consisting of at least one first purging period and at least one second purging period. In other words, though the certain purging period of the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref> consists of consecutive n times of the first purging period and subsequently consecutive m times of a period necessary for the sequence in which the first purging period follows the second purging period. As long as the certain purging period substantially consists of at least one first purging period and at least one second purging period, there may exist non-purging period, in which no purging is performed, between the two consecutive purging periods in the certain purging period or between two consecutive sequences. In the case where the first purging period and the second purging period are defined above, in the purging pattern of <figref idref="DRAWINGS">FIG. 8</figref>, the certain purging period includes the first purging period greater in number than the second purging period, and the first purging is a purging performed in the last purging period among a plurality of purging periods included in the certain purging period. Furthermore, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, two consecutive second purgings are not performed in the certain purging period, i.e., two second purging periods are not consecutive. More specifically, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, in the certain purging period, the first purging is performed following the second purging. Moreover, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, in the certain purging period, the first purging is performed consecutively at least twice, i.e., the first purging period continues at least twice. Further, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, at the end of the certain purging period, the sequence in which the first purging is performed following the second purging is performed at least once. In other words, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, as the last two purgings in the certain purging period, the second purging and the first purging following the second purging are performed. Described in another way, in the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>, the second purging and the first purging are respectively performed in the last two purging periods among the plurality of purging periods included in the certain purging period, and the first purging is performed following the second purging in the last purging period.

0060After executing of S<b>3</b>, the controller <b>1</b><i>p </i>controls the cap <b>40</b> to be positioned at the capping position (S<b>4</b>). The controller <b>1</b><i>p </i>first controls the opposing member <b>42</b> to move from the second position to the first position by driving of the opposing-member lifting motor <b>42</b>M. The controller <b>1</b><i>p </i>then makes the support mechanism <b>5</b> keep at the open position and the opposing member <b>42</b> at the first position and the annular-member lifting motor <b>41</b>M (shown in <figref idref="DRAWINGS">FIG. 6</figref>) drive the gears <b>43</b> to rotate such that the annular member <b>41</b> moves down. Accordingly, the lower end <b>41</b><i>a </i>of the annular member <b>41</b> comes into contact with the opposing surface <b>42</b><i>a </i>such that the ejection space V<b>1</b> is defined between the opposing surface <b>42</b><i>a </i>and the ejection surface <b>10</b><i>x. </i>

0061The controller <b>1</b><i>p </i>ends the routine after executing of S<b>4</b>.

0062As mentioned above, in the present embodiment, in the certain purging period constituted by the combination of the at least one Bk purging and the at least one Pr purging, the Bk purgings are greater in number of times than the Pr purging. Therefore, a discharging amount of the pretreatment liquid can be reduced. Further, because the Bk purging is performed as the last purging in the certain purging period, a time period when the head <b>10</b><i>b </i>waits in a state of being uncapped by the cap <b>40</b> at the end of the certain purging period can be decreased. Thus, the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>b </i>is restrained from drying.

0063In a case where the Pr purging is consecutively performed in the certain purging period, drying of the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>b </i>is getting worse in the consecutive Pr purgings. On the other hand, in the present embodiment, since the two Pr purgings are not consecutively performed in the certain purging period, the drying of the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>b </i>can be restrained.

0064Because the two Bk purgings are consecutively performed in the certain purging period, decreasing of the discharging amount of the pretreatment liquid and the recovery of the ejection performance of the head <b>10</b><i>b </i>can be effectively compatible with each other.

0065In a case where the two Bk purgings are consecutively performed at the end of the certain purging period, drying of the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>a </i>is getting worse in the consecutive Bk purgings. On the other hand, in the present embodiment, since the sequence in which the Bk purging is performed following the Pr purging is performed once or a plurality of numbers of times at the end of the certain purging period, the drying of the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>a </i>in addition to the drying of the nozzles <b>14</b><i>a </i>of the head <b>10</b><i>b </i>can be prevented.

0066Hereinafter, inkjet printers as a second and a third embodiments to which the present invention is applied will be described.

0067The printers in the second and the third embodiments have the same structure as the printer <b>1</b> in the first embodiment, except that the pumps <b>10</b>Pa, <b>10</b>Pb are driven to execute respective purging patterns shown in <figref idref="DRAWINGS">FIGS. 8B</figref>, <b>8</b>C instead of the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref>.

0068In the purging pattern of <figref idref="DRAWINGS">FIG. 8B</figref> in the second embodiment, first, the sequence in which the Bk purging is performed following the Pr purging is performed m times, and then the Bk purging is performed consecutively m times, and thereafter the sequence in which the Bk purging is performed following the Pr purging is performed m times. The purging pattern of <figref idref="DRAWINGS">FIG. 8B</figref> is common to the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref> in that (A) in the certain purging period, the Bk purgings are performed in greater number of times than the Pr purgings and (B) the Bk purging is performed as the last purging in the certain purging period, (C) the two Pr purgings are not consecutively performed in the certain purging period, (D) the Bk purgings are consecutively performed in the certain purging period, and (E) the sequence in which the Bk purging is performed following the Pr purging is performed once or plural times at the end of the certain purging period.

0069In the purging pattern of <figref idref="DRAWINGS">FIG. 8C</figref> in the third embodiment, first, the sequence in which the Bk purging is performed following the Pr purging is performed m times, and then the Bk purging is performed consecutively m times. The purging pattern of <figref idref="DRAWINGS">FIG. 8C</figref> is common to the purging pattern of <figref idref="DRAWINGS">FIG. 8A</figref> in that (A) in the certain purging period, the Bk purgings are performed in greater number of times than the Pr purging and (B) the Bk purging is performed as the last purging in the certain purging period, (C) the two Pr purgings are not consecutively performed in the certain purging period, and (D) the two Bk purgings are consecutively performed in the certain purging period.

0070The second and the third embodiments, having the same structure as the first embodiment, enjoy the similar effects as the first embodiment has.

0071The present invention is not limited to the illustrated embodiments. It is to be understood that the present invention may be embodied with various changes and modifications that may occur to a person skilled in the art, without departing from the spirit and scope of the invention defined in the appended claims.

0072The first head and the second head may be of any numbers that are not less than 1. The first and the second heads may be serial-type heads, instead of the line-type heads. The first liquid may be a pigment ink of color, and may be any other liquid as long as the liquid contains pigments. The second liquid may be, not limited to the above-described pretreatment liquid, an aftertreatmemt liquid that lands on a recording medium after the first liquid lands thereon, or may be any other liquid as long as the liquid contains no pigments.

0073A cap is not limited to be composed of the annular member <b>41</b> and the opposing member <b>42</b>. For example, the cap may be composed of a single member having a concave shape which covers the ejection surface <b>10</b><i>x </i>from under the ejection surface <b>10</b><i>x</i>. This type of cap is, for example, made of a flexible material such as rubber as a whole and consists of a bottom portion and a lip portion which stands from an outer circumference of the bottom portion. When the cap is positioned at the capping position, an upper end of the lip portion is in contact with the ejection surface <b>10</b><i>x</i>, and a space between the ejection surface <b>10</b><i>x </i>and the bottom portion is defined by the lip portion as an ejection space. In a case of this type of cap, because the bottom portion and the lip portion are integral with each other, a plurality of lifting mechanisms are unnecessary. Further, since the bottom portion functions as the opposing member in the illustrated embodiments, there is no need to dispose an opposing member independently. Furthermore, especially in a case of this type of cap, a suction purging (a type of purging in which inside of the cap is sucked to negative pressure such that liquid is discharged from nozzles by suction power) may be adopted, instead of a pressurized purging (a type of purging in which liquid is supplied to a head by a pump such that liquid is discharged from nozzles) as in the illustrated embodiments. Furthermore, this type of cap may have a function to prevent viscosity of liquid in the nozzles, as well as a function to receive liquid discharged by a purging operation. If there is enough room for placement, a cap having a function to receive liquid discharged by a purging operation and a cap having a function to prevent viscosity of liquid in the nozzles may be disposed independently.

0074Though the wiping operation is performed after each purging in the illustrated embodiments, from viewpoint for reduction of time, a wiping operation may be performed only after the last first purging and second purging in the purging pattern (e.g., the last Pr purging and Bk purging in <figref idref="DRAWINGS">FIG. 8A</figref>). The two first purgings may not be performed successively in the certain purging period. Further, the two second purgings may be performed successively in the certain purging period.

0075A recording medium, not limited to the recording sheet P, may be any medium that is recordable. A liquid ejection apparatus is not limited to a printer, and may be a facsimile machine, a copier machine, or the like.